In the past, women who suffered spontaneous abortions were advised to wait at least 3 months and often 6, before attempting future pregnancies. The reasoning? “To give their bodies time to heal.” The World Health Organization has recommended delaying pregnancy for 6 months after a miscarriage to achieve optimal outcomes in the next pregnancy. The professional justification was that the time was needed for the woman (and her partner) to grieve. Does delaying a pregnancy after miscarriage really help? And come to think of it, how about delaying pregnancy after an abortion? These questions beg the further question: what is the current thinking on interpregnancy intervals in general?

Today it is quite clear that routine delays are not needed. A large systematic review and meta-analysis of 16 studies involving 1,043,840 women showed that a short interpregnancy interval following miscarriage actually was associated with a slightly reduced risk of future miscarriage and preterm labor and no increase in stillbirth, low birthweight, or pre-eclampsia.[1] Occasionally, a woman who miscarries may need an opportunity to optimize her health: to achieve good glucose control, to switch medications, to update her vaccinations, or to have 1-3 months of taking folic acid. She will need time to deal with those issues before the next pregnancy. But for a healthy woman desiring pregnancy, who has been evaluated and found to have no remaining needs, advise her to continue taking her prenatal vitamins and to avoid coitus just until her bleeding stops. Ovulation detection kits may help the couple more effectively achieve their reproductive goals.

A variation on the question would be: What is the optimal interval following pregnancy termination? Männistö, et al., looked at this question, using an older cross-sectional study design. They studied 19,894 women who underwent pregnancy termination between 2000 and 2009 and whose subsequent pregnancy ended in a live singleton delivery.[2] They reported that even after adjusting for nine background factors, an interpregnancy interval of less than 6 months was associated with a slightly increased risk of preterm birth OR = 1.35 (95% CI 1.02-1.77), but no other neonatal or maternal adverse events were found.

What about the timing after a delivery? In the past, the World Health Organization recommended that a woman wait 2 years from the delivery of one pregnancy to the conception of a subsequent one. Earlier studies had demonstrated that shorter intervals (>18 months) and longer ones (> 59 months) were associated with increased risks of preterm birth, low birth weight, small for gestational age birth, and neonatal intensive care admissions.[3],[4],[5],[6],[7] Longer inter-pregnancy intervals also have been associated with increased risk of pre-eclampsia.[8] These findings were based on cross-sectional studies in which the outcomes of mothers with short interpregnancy intervals were compared with the outcomes of pregnancies in women who had the so-called optimal interpregnancy intervals.

Now, however, researchers have taken a fresh look at how to study the issue in a way that could give a more true answer. Instead of taking the approach of cross-sectional studies that look at different women who had different interpregnancy intervals, researchers are looking at how individual women’s multiple pregnancies may be affected by their own different interpregnancy intervals. Three large studies have studied large cohorts of women who themselves had three or more deliveries and could provide two interpregnancy intervals.[9],[10],[11] Most recently, Hanley, et al., compared the outcomes of pregnancies that occurred at shorter time intervals (0-5, 6-11, and 12-17 months) after the prior pregnancy to the outcomes of pregnancies that occurred following the presumed optimal period (18-24 months). Similarly, they compared the outcomes of pregnancies after optimal intervals (18-23 months) to those after longer intervals (24-59 and > 60 months). They studied both adverse neonatal outcomes (birth < 37 weeks’ gestational age, birth weight < 10th percentile for < 2500 g, NICU use) and adverse maternal outcomes (gestational diabetes, BMI ? 30 kg/m2 pre-pregnancy weight, and preeclampsia.)

First, they undertook the traditional analysis (in which outcomes of women with different interpregnancy intervals were compared to each others’ rather than to their own). Using that traditional approach, they found what has been reported in earlier work—that the risk of prematurity was increased in short-interval pregnancies. But when they used the new approach (where the outcomes of women were compared to their own earlier outcomes), they reach a very different result: all the neonatal risks from short-interval pregnancies disappeared. However, some of the maternal risks continued; women with very short interpregnancy intervals (less than 12 months) had higher rates of beginning the next pregnancy with a BMI ? 30 kg/m2 and of developing gestational diabetes during that pregnancy.

While these studies are very reassuring about the neonatal outcomes after close pregnancy spacing, these studies do not measure the impact of a short interpregnancy interval on the health and well-being of the infant born from the preceding pregnancy. With a short interval, will breastfeeding of that first infant have to be stopped early? Will that infant have adequate exposure to parental attention before a sibling diverts that attention to himself?

Even in the face of these potential adverse impacts on the first infant, these studies are very germane for an increasingly large segment of reproductive-age women—older women who have delayed their childbearing. To ask a 41-year-old woman to wait another 18-24 months before she starts another pregnancy may be very difficult, especially if her fertility is dropping precipitously. Her chance of conceiving and carrying a healthy pregnancy after waiting 2 years diminishes dramatically. For women who step out of the work force to have their children, more prolonged delays may diminish their ability to return to work or to achieve their ultimate professional goals. With these new insights, women who have only short time periods to start their families—for any reason—may be reassured that they will not face higher risks with interpregnancy intervals that are shorter than those that have traditionally been advocated. As Klebanoff concluded in a recent editorial:

“Women whose pregnancies were uncomplicated and who are in good health can be advised that their decisions regarding timing of subsequent pregnancies should be based primarily on personal desire regarding child spacing and ultimate family size and only secondarily on obsolete concerns.”[12]

How can we spread this good news?

Submitted by: Anita Nelson, MD, professor emeritus of obstetrics and gynecology at the David Geffen School of Medicine at the University of California-Los Angeles and clinical professor at the University of Southern California

Contraceptive Technology

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This month’s clinical pearl

December 2018 Clinical Fact:

“Because implants and IUDs are highly effective, they are excellent choices for the short-term, too, and the fact that an implant or an IUD is good for “up to” 3 to 20 years is an added advantage but not always relevant.” — Contraceptive Technology, 21st edition